Physical layer device having a serdes pass through mode

ABSTRACT

A physical layer device (PLD), comprising: a first serializer-deserializer (SERDES) device having a first parallel port; a second SERDES device having a second parallel port; a third SERDES device having a third parallel port; and a path selector being selectively configurable to provide either (i) a first signal path between the first and second parallel ports, or (ii) a second signal path between the first and third parallel ports.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application No. 60/398,614, filed Jul. 26, 2002, entitled “A Physical Layer Device Having a Serdes Pass Through Mode,” which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates generally to data communications.

[0004] 2. Background

[0005] A data communication network includes multiple communication devices and a connection infrastructure or medium for interconnecting or networking the communication devices. The communication devices may include stand-alone computers or embedded controllers. Often, the communication devices include or connect with high-speed analog serial data interfaces or ports configured to operate at Gigabit-per-second (Gbps) data rates. Typically, the serial data interfaces are configured in accordance with known data transmission standards, such as optical fiber and copper wire Ethernet standards. Therefore, there is a need for a connection infrastructure capable of interfacing with such high-speed analog serial data interfaces. It is desirable that the connection infrastructure be capable of operating at the Gigabit-per-second data rates, and in accordance with the different transmission standards.

[0006] At any given time, only a subset, such as two, of the communication devices may need to communicate with each other. A direct data connection or path between the two communication devices facilitates high-speed data communication. Over time, different subsets of communication devices require different direct path connections. Therefore, it is desirable that the connection infrastructure be capable of being selectively configurable to provide the different direct path connections between communication devices.

SUMMARY

[0007] In an embodiment, the present invention is directed to a communication infrastructure or medium, referred to herein as a physical layer device (PLD), for selectively interconnecting multiple communication devices through high-speed serial data interfaces. The PLD supports high-speed serial data exchanges between the communication devices, at gigabit-per-second data rates. The PLD supports different data transmission interfaces and standards, such as Ethernet optical fiber and copper line serial data interface standards. The PLD is capable of being selectively configurable to provide different direct path connections between different communication devices.

[0008] In an embodiment, the PLD is constructed on a integrated circuit (IC) chip, and includes a first serializer-deserializer (SERDES) device having a first parallel port. The first SERDES device also includes a first serial port coupled to a first communication device. The PLD includes a second SERDES device having a second parallel port. The second SERDES device also includes a second serial port coupled to a second communication device. The PLD also includes a third SERDES device having a third parallel port. The third SERDES device also includes a third serial port coupled to a third communication device. The PLD further includes a path selector that is selectively configurable to provide either (i) a first signal path for routing first deserialized data between the first and second parallel ports, or (ii) a second signal path for routing second deserialized data between the first and third parallel ports. Thus, the first and second communication devices can communicate through the first SERDES devices and the path selector, while the first and third communication devices can communicate through the first and third SERDES devices and the path selector.

[0009] Further embodiments, features, and advantages of the present invention, as well as the structure and operation of the various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

[0010] The accompanying drawings/Figures, which are incorporated herein and form a part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention. In the drawings, like reference numbers indicate identical or functionally similar elements. In the drawings, the indicators “D,” “S,” “d” and “c” respectively indicate or represent “Deserializer,” “Serializer,” “data signal,” and “clock signal.”

[0011]FIG. 1 is a block diagram of an example system in which an example physical layer device (PLD) may operate.

[0012]FIG. 2A is a block diagram of a portion of the PLD of FIG. 1, corresponding to when a path selector of the PLD is in a first configuration.

[0013]FIG. 2B is a block diagram of a portion of the PLD of FIG. 1, corresponding to when the path selector is in a second configuration.

[0014]FIG. 3 is a block diagram of an example arrangement of the path selector.

DETAILED DESCRIPTION OF THE INVENTION

[0015]FIG. 1 is a block diagram of an example system 100 in which embodiments of the present invention may operate. System 100 includes a physical layer device (PLD) 102 operated and constructed in accordance with the present invention. In an embodiment, PLD 102 is constructed on a single integrated circuit (IC) substrate or chip. PLD 102 may be implemented in Complementary Metal Oxide Semiconductor (CMOS) technology, for example. Other semiconductor technologies may be used.

[0016] PLD 102 includes multiple input/output (I/O) ports 104, 106 and 108. I/O ports 104-108 represent connectors, conductive traces, PLD I/O pins, receivers and drivers, and the like, associated with coupling signals to and from PLD 102. PLD 102 includes a serializer-deserializer (SERDES) device 110 coupled to I/O port 104, a SERDES device 112 coupled to I/O port 106, and a SERDES device 114 coupled to I/O port 108. Each SERDES device includes (i) a transmitter/serializer (S) for serializing a parallel data signal, to produce a serial data signal, and (ii) a receiver/deserializer (D) for deserializing a serial data signal, to produce a parallel data signal, as is described in detail below. PLD 102 also includes a path selector 116 coupled between SERDES devices 110, 112 and 114, and a controller 118 for controlling path selector 116.

[0017] PLD 102 interfaces with a communication or network device 120 through I/O port 104 and a high-speed analog serial data interface 122 (where the I/O port and the data interface are collectively referred to as a serial interface of PLD 102). Network device 120 may be a Media Access Controller (MAC). Serial data interface 122 includes bi-directional serial data signals 122 a and 122 b, and a clock signal 122 c synchronized with serial data signal 122 b. Bi-directional serial data signals 122 a and 122 b have example baud rates of 1.25 Gbps, and clock signal 122 c has a corresponding example clock rate or frequency of 1.25 GHz.

[0018] PLD 102 interfaces with an optical fiber module 124 through I/O port 106 and a high-speed analog serial data interface 126 (where the I/O port and the data interface are collectively referred to as a serial interface of PLD 102). High-speed serial data interface 126 includes bi-directional analog serial data signals 126 a and 126 b having example baud rates in the gigabit-per-second range. Serial interface 126 also includes a clock signal 126 c synchronized with and having a frequency commensurate with serial data signal 126 b. Optical fiber module 124 interfaces with an optical line 127. Optical fiber module 124 may operate in accordance with IEEE 802.3 for 1000 Base-X, for example.

[0019] SERDES device 114 interfaces with a communication or network device 128 through I/O port 108 and a high-speed analog serial data interface 130 (where the I/O port and the data interface are collectively referred to as a serial interface of PLD 102). Serial data interface 130 includes bi-directional serial data signals 130 a and 130 b having baud rates in the Gbps range. Serial data signals 130 a and 130 b may be carried over a copper line associated with an Ethernet link, for example, coupled to I/O port 108. SERDES device 114 may be an Ethernet transceiver that operates in accordance with IEEE 802.3 for 10/100/1000 Base-T, for example. It is understood that optical fiber module 124 and SERDES device 114 are exemplary and may be replaced by a multitude of other interface devices in other arrangements of the present invention. For example, SERDES device 112 and optical system 124 and 127 may be replaced with a transceiver and an associated interface suitable for copper-based signals, while SERDES device 114 and associated interface 130 may be replaced by a transceiver and interface suitable for optical signals, and so on.

[0020] SERDES device 110 includes a deserializer 110 a and a serializer 110 b. Deserializer 110 a includes a deserializer input 140, a clock and data recovery module 142, and deserializer output 144. In operation, communication device 120 transmits serial data signal 122 a to deserializer input 140. Clock and data recovery module 142 deserializes serial data signal 122 a received at deserializer input 140, to produce a deserialized data signal 146. The terms “deserializes” and “deserializing” mean to convert serial data to parallel data. Clock and data recovery module 142 recovers a clock signal 148 from received serial data signal 122 a. Recovered clock signal 148 represents received signal timing, for example, the timing of data symbols included in received serial data signal 122 a. Deserializer 110 a transmits signals 146 and 148 from deserializer output 144. Clock signal 148 is synchronous with data signal 146.

[0021] Clock and data recovery module 142 generates deserialized data signal 146 as a series of N1-bit wide parallel digital data words, having a data rate equal to R1/N1, where R1 is the data rate of received serial data signal 122 a. Thus, the aggregate data rate of deserialized data signal 146 is equal to the data rate of serial data signal 122 a. Module 142 generates clock signal 148 synchronously with deserialized data signal 146, and at a frequency equal to R1/N1. In an example arrangement, N1=10 and R1=1.25 GHz. Thus, serial data signal 122 a has a data rate of 1.25 GHz, module 142 generates 10-bit parallel words at a data rate of 125 MHz (1.25 GHz=10 times 125 MHz), and clock signal 148 has a frequency of 125 MHz.

[0022] Serializer 110 b includes a serializer input 150, a serializer and clock generator module 152, and a serializer output 153. In configurations to be described below, path selector 116 provides a deserialized data signal 154 and an associated clock signal 156 to deserializer input 150. Serializer and clock generator 152 serializes deserialized data signal 154 in accordance with clock signal 156, to produce serialized data signal 122 b. The terms “serializes” and “serializing” mean to convert parallel data to serial data. Serializer and clock generator 152 also produces clock signal 122 c synchronous with serial data signal 122 b. Serializer 110 b transmits signals 122 b and 122 c from serializer output 153.

[0023] In an example arrangement, deserialized data signal 154 includes a series of N2-bit wide parallel digital data words, having a data rate equal to R2/N2, where R2 is the data rate of received serial data signal 126 a. Thus, the aggregate data rate of deserialized data signal 154 is equal to the data rate of serial data signal 126 a. Also, clock signal 156 is synchronous with deserialized data signal 154, and has a frequency equal to R2/N2. In an example arrangement, N2=10 and R2=1.25 GHz. Thus, serial data signal 126 a has a data rate of 1.25 GHz, data signal 154 includes 10-bit parallel words at a data rate of 125 MHz (1.25 GHz=10 times 125 MHz), and clock signal 156 has a frequency of 125 MHz. Based on these data and clock rates, serializer 152 generates serial data signal 122 b at a data rate of 1.25 GHz, and clock signal 122 c at a frequency of 1.25 GHz.

[0024] The terms “deserialized” and “parallel” are used equivalently and interchangeably herein. Also, a deserializer output is a parallel data output and a serializer input is a parallel data input. Together, a deserializer output (e.g., deserializer output 144) and a serializer input (e.g., serializer input 150) represent a parallel port of a SERDES device (e.g., a parallel port of SERDES device 110). Similarly, a deserializer input (e.g., deserializer input 140) and a serializer output (e.g., serializer output 153) collectively represent a serial port of a SERDES device (e.g., a serial port of SERDES device 110).

[0025] SERDES 112 includes a deserializer 112 a and serializer 112 b. Deserializer 112 a includes a serializer input 158, a clock and data recovery module 160 and a deserializer output 162. Deserializer 112 a operates in substantially the same way as deserializer 110 a. Serializer input port 158 receives serial data signal 126 a. Clock and data recovery module 160 deserializes received serial data signal 126 a, to produce deserialized or parallel data signal 164. Module 160 also recovers a clock signal 166 from received serial data signal 126 a. From deserializer output 162, deserializer 112 a transmits signals 164 and 166 to path selector 116.

[0026] Serializer 112 b operates in substantially the same way as serializer 110 b. In configurations to be described below, path selector 116 provides a deserialized or parallel data signal 174 and its associated clock signal 176 to serializer input 168. Serializer and clock generator module 170 serializes deserialized data 174 in accordance with clock signal 176, to produce serial data signal 126 b and its associated clock signal 126 c. Data signal 126 b and clock signal 126 c have example data and clock rates in the GHz range. Together, deserializer output 162 and serializer input 168 represent a parallel port 177 of SERDES device 112. SERDES device 112 supports example data rates and uses parallel data bit-widths similar to or the same as those of SERDES device 110, mentioned above. In an alternative arrangement, module 170 generates only a serial data signal that essentially encapsulates both data and clock signals 126 b and 126 a.

[0027] SERDES 114 includes a deserializer 114 a and a serializer 114 b. Serializer 114 a include a serializer input 178 and a serializer output 180. Deserializer 114 b includes a deserializer input 184 and a deserializer output 182. In configurations to be described below, path selector 116 provides a deserialized data signal 186 to serializer input 178. Serializer 114 a serializes deserialized data signal 186 into serialized data signal 130 a, and transmits the serialized data signal from serializer output 180. Deserializer 114 b receives serial data signal 130 b at deserializer input 184. Deserializer 114 b deserializes serial data signal 130 b, to produce deserialized data signal 188. Deserializer 114 b transmits deserialized data signal 188 to path selector 116, from deserializer output 182. Together, deserializer output 182 and serializer input 178 represent a parallel port 189 of SERDES device 114. SERDES device 114 may support example data rates similar to or the same as those of SERDES devices 110 and 112, mentioned above. SERDES device 114 may support parallel data bit-widths different from those used with SERDES devices 110 and 112, for the reason discussed below in connection with FIG. 3. In another embodiment, SERDES device 114 generates clock signals associated with data signals in a manner similar to SERDES devices 110 and 112.

[0028] Controller 118 provides a control signal 190 to path selector 116. Control signal 190 selects alternative first and second configurations of path selector 116. That is, path selector 116 is selectively configurable responsive to control signal 190. At a high level, path selector 116 can be considered to include a switch having connection nodes 192, 193 and 194, respectively coupled to parallel ports 159, 177 and 189. The switch has selectable first and second positions corresponding to the first and second configurations mentioned above.

[0029] The first switch position (depicted in FIG. 1) couples together nodes 192 and 193, while the second position couples together nodes 192 and 194. Thus, in the first switch position, selector 116 couples parallel port 159 to parallel port 177, whereby bi-directional de-serialized data signals and their associated clock signals are routed between these parallel ports. This configuration is referred to as a SERDES pass-through mode. Alternatively, in the second switch position, selector 116 couples parallel port 159 to parallel port 189, whereby bi-directional serial data signals are routed between these parallel ports. Thus, path selector 116 is selectively configurable to provide either:

[0030] (i) in a first configuration, a bi-directional signal path between parallel port 159 of SERDES device 110 and parallel port 177 of SERDES device 112; or

[0031] (ii) in a second configuration, a bi-directional signal path between parallel port 159 of SERDES device 110 and parallel port 189 of SERDES device 114.

[0032] The bi-directional signal paths provided by path selector 116 carry parallel data, and clock signals when appropriate, between the respective parallel ports of SERDES devices 110, 112 and 114. The first configuration of path selector 116 essentially interconnects communication or network devices 120 and 124, whereby these devices can exchange data with each other at Gbps data rates, through PLD 102. More specifically, devices 120 and 124 exchange data through their respective serial interfaces, SERDES devices 110 and 112, and path selector 116.

[0033] The second configuration of path selector 116 essentially interconnects communication or network devices 120 and 128, whereby these devices can also exchange data at Gbps data rates through their respective serial interfaces, SERDES devices 110 and 114, and path selector 116. From the perspective of device 120, PLD 102 provides a single IC chip connection infrastructure that selectively interconnects device 120 to either of devices 124 and 128, through the single serial interface (122) of device 120. This reduces the number of communication ports associated with device 120, and the number of I/O pins required on any communication port of device 120 that interfaces with PLD 102.

[0034]FIG. 2A is a block diagram of a portion of PLD 102 corresponding to when path selector 116 is in, or set to, the first configuration. In the first configuration, path selector 116 provides bi-directional signal paths 204 a and 204 b (collectively, bi-directional signal path 204) for routing signals between parallel port 159 of SERDES device 110 and parallel port 177 of SERDES device 112. Specifically, signal path 204 a routes data and clock signals 164 and 166 from deserializer output 162 to serializer input 150. In the first configuration, data signals 154 and 164 are the same and clock signals 156 and 166 are the same. Also, signal path 204 b routes data and clock signals 146 and 148 from deserializer output 144 to serializer input 168. In this configuration, deserialized data signals 174 and 146 are the same and recovered clock signals 176 and 148 are the same.

[0035]FIG. 2B is a block diagram of a portion of PLD 102 corresponding to when path selector 116 is in the second configuration. In the second configuration, path selector 116 provides bi-directional signal paths 210 a and 210 b (collectively, bi-directional signal path 210) for routing bi-directional deserialized data signals between parallel port 159 and parallel port 177. Specifically, signal path 210 a routes data signal 188 from deserializer output 182 to serializer input 150. In the first configuration, data signals 188 and 154 carry the same data content. Also, signal path 204 b routes data signal 146 from deserializer output 144 to serializer input 178. In this configuration, deserialized data signals 146 and 186 carry the same data content. In the second configuration, path selector 116 generates clock signal 156 synchronous with data signal 154, in the manner described below in connection with FIG. 3.

[0036]FIG. 3 is a block diagram of an example arrangement of path selector 116. All of the data signal paths depicted in FIG. 3 are parallel data paths. Path selector 116 includes a plurality of multiplexers or selectors 304, 306 and 308, and a digital processor section 310 (also digital section). Controller 118 configures each of the mutiplexers or selectors 304-308 and digital section 310 as appropriate to set path selector 116 in either the first configuration or the second configuration, according to control signal 190. Thus, mutiplexers 304, 306 and 308 are collectively referred to herein as multiplexer logic that is configurable to support either the first or second configuration according to control signal 190.

[0037] Controller 118 sets control signal 190 to either a first value or a second value to respectively set path selector 116 to either the first configuration or the second configuration. For example, in an arrangement where control signal is a digital signal, controller 118 sets control signal to either a logic “0” or a logic “1” to respectively configure path selector 116 in either the first configuration or the second configuration. Alternatively, the polarity of control signal 190 may be reversed. In another arrangement, controller 118 generates multiple control signals.

[0038] Digital section 310 includes digital control and signal processing logic to perform exemplary functions such as data encoding, data packetizing, data decoding and data depacketizing, when path selector 116 is set to the second configuration, as described below. Digital section 310 also includes an enable circuit (not shown) to selectively disable or enable the operation of the digital section responsive to control signal 190, when path selector 116 is in the first and second configurations, respectively. In an arrangement, the enable circuit is a switch, connected between a power supply rail of PLD 102 and operational circuits of digital section 310, responsive to control signal 190. The switch removes power from the operational circuits of digital section 310, to disable the digital section, when path selector 116 is set to the first configuration. In the second configuration, the switch applies power to the operational circuits of digital section 310, to enable the digital section.

[0039] When control signal 190 sets path selector 116 to the first configuration, the path selector operates as follows. Multiplexer 304 passes deserialized data signal 146 to serializer 112 b, as deserialized data signal 174. Multiplexer 306 passes deserialized data signal 164 to serializer 110 b, as deserialized data signal 154. Multiplexer 308 passes clock signal 166 to serializer 110 b, as clock signal 156. Clock signal 148 passes from deserializer 110 a, directly through path selector 116, to serializer 112 b. Thus, the first signal path through path selector 116 includes multiplexers 304, 306 and 308 configured as just described.

[0040] When control signal 190 sets path selector 116 to the second configuration, the path selector operates as follows. Multiplexer 304 passes deserialized data signal 146 to an input of digital section 310, as data signal 311. Digital section 310 processes deserialized data signal 311/146, to produce deserialized data signal 186. For example, digital section 310 may reformat deserialized data signal 146 by removing error correction and packet protocol bits from deserialized data signal 146. Digital section 310 also receives deserialized data signal 188 from deserializer 114 b. Digital section 310 generates a deserialized data signal 314 from deserialized data signal 188. For example, digital section 310 may reformat deserialized data signal 188 by adding error correction and packet protocol bits to the signal 188.

[0041] Multiplexer 306 passes deserialized data signal 314 to serializer 110 b, as deserialized data signal 154. Digital section 310 generates a data clock 316 synchronous with deserialized data signal 314. Multiplexer 308 passes data clock 316 to serializer 110 b, as clock signal 156. Thus, the second signal path through path selector 116 includes multiplexers 304, 306 and 308, and digital section 310, configured as just described.

CONCLUSION

[0042] While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention.

[0043] The present invention has been described above with the aid of functional building blocks illustrating the performance of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed. Any such alternate boundaries are thus within the scope and spirit of the claimed invention. One skilled in the art will recognize that these functional building blocks can be implemented by analog and/or digital circuits, discrete components, application specific integrated circuits, firmware, processors executing appropriate software and the like or any combination thereof. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents. 

What is claimed is:
 1. A physical layer device (PLD), comprising: a first serializer-deserializer (SERDES) device having a first parallel port; a second SERDES device having a second parallel port; a third SERDES device having a third parallel port; and a path selector being selectively configurable to provide either (i) a first signal path between the first and second parallel ports, or (ii) a second signal path between the first and third parallel ports.
 2. The PLD of claim 1, wherein each of the first, second and third parallel ports includes (i) a deserializer output for transmitting parallel, deserialized data, and (ii) a serializer input for receiving parallel data to be serialized.
 3. The PLD of claim 1, wherein the first signal path is configured to route (i) deserialized data signals between the first and second parallel ports, and (ii) at least one data clock, synchronized with at least one of the deserialized data signals, between the first and second parallel ports.
 4. The PLD of claim 1, wherein: the first signal path is configured to route a first deserialized data signal from the first parallel port to the second parallel port, and a first data clock, synchronized with the first deserialized data signal, from the first parallel port to the second parallel port; and the second SERDES device is configured to convert the first deserialized data signal into a first serial data signal according to the first data clock.
 5. The PLD of claim 4, wherein: the first signal path is also configured to route a second deserialized data signal from the second parallel port to the first parallel port, and a second data clock, synchronized with the second deserialized data signal, from the second parallel port to the first parallel port; and the first SERDES device is configured to convert the second deserialized data signal into a second serial data signal according to the second data clock.
 6. The PLD of claim 1, wherein the second signal path is configured to route (i) deserialized data signals between the first and third parallel ports, and (ii) at least one data clock, synchronized with at least one of the deserialized data signals, between the first and third parallel ports.
 7. The PLD of claim 1, further comprising: a controller configured to produce a path selector control signal, wherein the path selector is selectively configurable to provide either the first signal path or the second signal path responsive to the path selector control signal.
 8. The PLD of claim 1, wherein the path selector includes multiplexer logic configurable to establish either the first path or the second path.
 9. The PLD of claim 8, wherein the second path of the path selector includes a digital section configured to process deserialized data signals from the first and third parallel ports.
 10. The PLD of claim 1, wherein: the first SERDES device includes a first serial data input and a first serial data output coupled to a first serial interface of the PLD; the second SERDES device includes a second serial data input and a second serial data output coupled to a second serial interface of the PLD; and the third SERDES device includes a third serial data input and a third serial data output coupled to a third serial interface of the PLD.
 11. The PLD of claim 10, wherein the first serial interface is a media access control (MAC) interface.
 12. The PLD of claim 10, wherein the second serial interface is an optical fiber interface.
 13. The PLD of claim 10, wherein the third serial interface is a copper medium interface.
 14. The PLD of claim 1, wherein the first, second and third SERDES devices, and the path selector are all constructed on a common integrated circuit (IC) substrate.
 15. A physical layer device (PLD) for interconnecting first, second and third devices capable of communicating over respective first, second and third serial interfaces, comprising: a first Serializer-Deserializer (SERDES) device having a first serial port coupled to the first serial interface, and a first parallel port; a second SERDES device having a second serial port coupled to the second serial interface, and a second parallel port; a third SERDES device having a third serial port coupled to the third serial interface, and a third parallel port; a controller for generating a path selector control signal; and a path selector being selectively configurable, responsive to the path selector control signal, to provide either: (i) a first signal path configured to route between the first and second parallel ports first bi-directional deserialized data signals, and a data clock, synchronized with at least one of the first bi-directional deserialized data signals; or (ii) a second signal path configured to route between the first and third parallel ports second bi-directional deserialized data signals.
 16. The PLD of claim 15, wherein, when the path selector is configured to provide the first path, the first and second communication devices are able to exchange data with each other through the first and second serial interfaces, the first and second SERDES devices, and the path selector.
 17. The PLD of claim 16, wherein, when the path selector is configured to provide the second path, the first and third communication devices are able to exchange data with each other through the first and third serial interfaces, the first and second SERDES devices, and the path selector.
 18. The PLD of claim 15, wherein: the first SERDES device is configured to deserialize serial data from the first serial interface, to produce at the first parallel port one of the first bi-directional deserialized data signals; and the second SERDES device is configured to deserialize serial data from the second serial interface, to produce at the second parallel port another one of the first bi-directional deserialized data signals. 